We propose to: 1) Develop a new model system for neoplastic transformation by chemicals requiring metabolic activation. The test carcinogen will be administered to rats undergoing liver regeneration, the liver cells will be cultured, and neoplastic transformation will be scored. 2) Use the system that we have established for in vitro transformation, the C3H/10T1/2 cells, for the detection and quantification of transformation by surface morphological changes seen with the scanning electron microscope. 3) Study in the C3H/10T1/2 cell system, transformation, mutagenesis, DNA damage, and DNA repair produced by chemical carcinogens, to provide patterns of traits that can be used as new criteria for early identification of transformation.